How probable is it that the world will descend into the chaos of nuclear war?
Apparently, a lot more likely than we might think!
These are the countries know to have a stockpile of nuclear weapons: the USA, UK, Russia, France, China, North Korea, India and Pakistan with Israel believed to possess them but not admitting to it.
There are a number of other countries that are known or believed to be trying to obtain nuclear weapons and probably others that may already have some.
Other than the USA and Russia, most of the countries on the list have small stocks of weapons and an ability to deliver them to a distant target with a mature and stable weapons platform.
Others have limited means of delivery; in other words they may be able to fire a short or medium range missile but not reach distant targets.
Of course, there are also tactical nuclear weapons which may be delivered by means other than missiles. For instance, a cargo ship could deliver a weapon into a distant port for detonation - see RAND Center for Terrorism Risk Management Policy
Humanity has the ability to wipe itself out, along with much of the biosphere and can do so at the touch of a button.
Fortunately, only the USA and Russia have the numbers of weapons required to bring about an extinction level event but even China, with 300 weapons, could herald a nuclear winter if all of their weapons were to be detonated.
Is any of that likely?
Those who cannot remember the past are condemned to repeat it.George Santayana
Humans are notoriously bad at not learning from historical mistakes. Does that mean that nuclear war is likely?
The USA and Russia operate under the MAD protocol - "Mutually Assured Destruction", a phrase coined by John von Neumann meaning that starting a nuclear war is an unwinnable proposition - it is suicide and that thinking has maintained an uneasy peace for decades.
However, that does not mean that other actors would not start a nuclear war and, on even a small scale the consequences could be disastrous - the site below does a good job of explaining the possible outcomes...